Using techniques recently refined and validated in this laboratory, a detailed study is proposed to investigate the effects of controlled ventilation on cardiovascular function. Studies will be performed in chronically instrumented dogs and man. Cardiac dimensions will be measured with implanted pulse transit ultrasonic dimension transducers. Various arrays of transducers will be utilized to permit continuous calculation of right and left ventricular volumes. Cardiac pressures will be measured with matched high fidelity micromanometers. Aortic, pulmonary artery, and coronary blood flows will be obtained with implanted electromagnetic flow probes. Data acquisition and analysis will be performed with a DEC 11/23 digital computer system which is fully committed to these studies. The possible mechanisms of diminished cardiac output during mechanical ventilation include: Limitation of cardiac preload with shifting and capacitance blood volume to the systemic venous system, reflex depression of intrinsic myocardial function, the afterloading effects of airway pressure on the right ventricle, and leftward septal shiftinh which interferes with left ventricular performance. Each of these mechanisms can be precisely and quantitatively evaluated with the preparations described, and an overall unifying hypothesis generated. Experiments will be performed in the animals with conventional mechanical ventilation, positive end expiratory pressure, intermittent mandatory ventilation, and high frequency ventilation. After completion of studies in the normal cardiopulmonary system, acute changes in pulmonary compliance will be produced with an intravenous infusion of oleic acid. Experiments then will be repeated to assess the effects of positive airway pressure on biventricular function in the pathophysiologic setting. Studies also will be performed in patients after cardiac operations and results correlated to animal experiments. This project could resolve the controversy currently existing in the literature about the specific effects of airway pressure on cardiac function, and the results could be of direct utility to the management of patients requiring mechanical ventilatory support.